From d24d38ea50f9b13a216c6473d933cc9f4d12880e Mon Sep 17 00:00:00 2001
From: neargye <neargye@gmail.com>
Date: Mon, 8 Apr 2019 18:29:03 +0500
Subject: [PATCH] add is_unscoped_enum/is_scoped_enum

---
 README.md              | 28 ++++++++++++++++++++++++++++
 include/magic_enum.hpp | 32 ++++++++++++++++++++++++++++++--
 test/test.cpp          | 12 ++++++++++++
 3 files changed, 70 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 3a20c06..980e32b 100644
--- a/README.md
+++ b/README.md
@@ -27,6 +27,8 @@ Header-only C++17 library provides static reflection on enums, work with any enu
 * `enum_count` returns number of enum values.
 * `enum_name` obtains string name from enum value.
 * `enum_names` obtains string enum name sequence.
+* `is_unscoped_enum` checks whether type is an Unscoped enumeration.
+* `is_scoped_enum` checks whether type is an Scoped enumeration.
 
 ## Features
 
@@ -137,6 +139,32 @@ enum Color { RED = 2, BLUE = 4, GREEN = 8 };
   std::cout << color << std::endl; // "BLUE"
   ```
 
+* Checks whether type is an Unscoped enumeration.
+  ```cpp
+  enum сolor { red, green, blue };
+  enum class direction { left, right };
+
+  magic_enum::is_unscoped_enum<color>::value -> true
+  magic_enum::is_unscoped_enum<direction>::value -> false
+  magic_enum::is_unscoped_enum<int>::value -> false
+
+  // Helper variable template.
+  magic_enum::is_unscoped_enum_v<color> -> true
+  ```
+
+* Checks whether type is an Scoped enumeration.
+  ```cpp
+  enum сolor { red, green, blue };
+  enum class direction { left, right };
+
+  magic_enum::is_scoped_enum<color>::value -> false
+  magic_enum::is_scoped_enum<direction>::value -> true
+  magic_enum::is_scoped_enum<int>::value -> false
+
+  // Helper variable template.
+  magic_enum::is_scoped_enum_v<direction> -> true
+  ```
+
 ## Remarks
 
 * `magic_enum::enum_cast` returns `std::optional<E>`, using `has_value()` to check contains enum value and `value()` to get the enum value.
diff --git a/include/magic_enum.hpp b/include/magic_enum.hpp
index 969fe9f..a89502b 100644
--- a/include/magic_enum.hpp
+++ b/include/magic_enum.hpp
@@ -180,11 +180,39 @@ template <typename E>
   return std::nullopt; // Invalid value or out of range.
 }
 
-template<class E>
-using enable_if_enum_t = typename std::enable_if<std::is_enum_v<std::decay_t<E>>>::type;
+template<typename T>
+using enable_if_enum_t = typename std::enable_if<std::is_enum_v<std::decay_t<T>>>::type;
+
+template<typename T, bool = std::is_enum_v<T>>
+struct is_scoped_enum_impl : std::false_type {};
+
+template<typename T>
+struct is_scoped_enum_impl<T, true> : std::bool_constant<!std::is_convertible_v<T, std::underlying_type_t<T>>> {};
+
+template<typename T, bool = std::is_enum_v<T>>
+struct is_unscoped_enum_impl : std::false_type {};
+
+template<typename T>
+struct is_unscoped_enum_impl<T, true> : std::bool_constant<std::is_convertible_v<T, std::underlying_type_t<T>>> {};
 
 } // namespace magic_enum::detail
 
+// Checks whether T is an Unscoped enumeration type. Provides the member constant value which is equal to true, if T is an Unscoped enumeration type. Otherwise, value is equal to false.
+// https://en.cppreference.com/w/cpp/language/enum#Unscoped_enumeration
+template <typename T>
+struct is_unscoped_enum : detail::is_unscoped_enum_impl<T> {};
+
+template <typename T>
+inline constexpr bool is_unscoped_enum_v = is_unscoped_enum<T>::value;
+
+// Checks whether T is an Scoped enumeration type. Provides the member constant value which is equal to true, if T is an Scoped enumeration type. Otherwise, value is equal to false.
+// https://en.cppreference.com/w/cpp/language/enum#Scoped_enumerations
+template <typename T>
+struct is_scoped_enum : detail::is_scoped_enum_impl<T> {};
+
+template <typename T>
+inline constexpr bool is_scoped_enum_v = is_scoped_enum<T>::value;
+
 // Obtains enum value from enum string name.
 template <typename E, typename = detail::enable_if_enum_t<E>>
 [[nodiscard]] constexpr std::optional<E> enum_cast(std::string_view value) noexcept {
diff --git a/test/test.cpp b/test/test.cpp
index 67588d6..fc5a5a1 100644
--- a/test/test.cpp
+++ b/test/test.cpp
@@ -233,3 +233,15 @@ TEST_CASE("operator<<") {
   test_ostream(number::three, "three");
   test_ostream((number)0, "");
 }
+
+TEST_CASE("type_traits") {
+  REQUIRE_FALSE(magic_enum::is_unscoped_enum_v<Color>);
+  REQUIRE_FALSE(magic_enum::is_unscoped_enum_v<Numbers>);
+  REQUIRE(magic_enum::is_unscoped_enum_v<Directions>);
+  REQUIRE(magic_enum::is_unscoped_enum_v<number>);
+
+  REQUIRE(magic_enum::is_scoped_enum_v<Color>);
+  REQUIRE(magic_enum::is_scoped_enum_v<Numbers>);
+  REQUIRE_FALSE(magic_enum::is_scoped_enum_v<Directions>);
+  REQUIRE_FALSE(magic_enum::is_scoped_enum_v<number>);
+}